f2fs: use IPU for fdatasync

This patch fixes missing IPU condition when fdatasync is called.
With this patch, fdatasync is able to avoid additional node writes for recovery.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -202,7 +202,7 @@ int f2fs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	trace_f2fs_sync_file_enter(inode);
 
 	/* if fdatasync is triggered, let's do in-place-update */
-	if (get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
+	if (datasync || get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
 		set_inode_flag(fi, FI_NEED_IPU);
 	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	clear_inode_flag(fi, FI_NEED_IPU);